Found my rear...

[project74]

Well, after much thought and flip flopping, I finally decided on the direction of this rather vital piece of drivetrain. I found a C-body 9.25/3.23 suregrip unit complete except for brakes, that just had over $500 USD worth of work put into it in March of last year. It's currently in a '72 Charger project and has only moved on and off a trailer a few times since it was redone. Guy is switching to an 8.75 for the sake of easy gear swaps, something I'm not worried about with this boat. A 9.25 seems to be a much more practical way to go budget wise as well. Those 8.75's are a fortune comparatively!

After MUCH research I've discovered some rather interesting info too. The '70 to '72 Fury's were apparently the ONLY C-bodies to not use a C-body rear. Nope, they all had B-body dimension rears, hence my thinking my current diff was swapped in from a B. The Fury was the "smallest" of the big C's and it's rear track was narrower than the front by .1 inches. Every other full size had a wider rear track than front.

Installing the 9.25 will push my wheels out about .75" on each side but clearance will still be about 1.25". Should actually help things out a bit cosmetically and handling wise, though handling isn't the main goal here. I remember Jass saying he had a C 9.25 under his '71 Bee and it really filled out the wheel wells nicely. Should be more than strong enough to handle the future 440 too. :giggedy:

 

[Dr.Jass]

You have chosen wisely. :2thumbs:

It's a good, stout piece. It's considerably stronger than the 8.75", too--much more than the half-inch of ring-gear size would indicate. I've had the two diffs side by side and there's considerably more beef to the 9.25". It'll handle anything you plan to throw at it, no doubt, and unlike GM C-clip axles and the 8.25" Chrysler, the 9.25" has an excellent record for durability. I've never seen one fail a C-clip.

It's definitely not the original axle in the '72 Charger, since to my knowledge the 9.25" wasn't available in B-bodies until '73 or '74.

Now for the warnings:

Before you buy, pull the cover and inspect the diff. It's a Borg-Warner cone-type unit, and since the parting line for the case halves runs through the pin bore, they're known to fail in the pin-bore area just like the 8.75" units. The only way to know is to look; I had about 190K miles on my '72 Charger's 8.75" rear. It made no noise, and the Sure Grip worked perfectly right up through the day I stopped driving it. I sold that axle to Stretch, and when he pulled it apart he found the pin bore was ovalled quite badly. The only repair is to replace the diff, so pull that cover before you plunk down your money. Obviously, look for excessive shavings while you're in there. It's not uncommon to find some silver since the cone-type diffs wear on the inside of the case directly, but if it looks like Nevr-Seez, keep on shopping.

Also before money changes hands, test the Sure Grip. Jack the car up or put the axle on sawhorses with wheels and tires installed, and have someone try to hold one tire. Without warning, give your tire a good, quick rotational yank. If the other guy doesn't lose his balance or outright fall down, the SG's worn. Again, the only fix is a new diff.

Check how well the axle's centered in the car if you can; if not, measure the distances from the center of the spring perch to the backing plate on both sides. One would think this is an automatic thing, but I've seen more than one Mopar where the axle's not even close to being centered. The first one was my high-school best friend's '74 Cuda. The 8.75" axle in that car was off center by almost 2 inches! One wheel filled the well nicely, the other seemed to sort of get lost in the opening. If the price is right, it's not a big deal to cut off the old and weld on new perches since they're cheap (around $25 for a pair) but if you're paying premium moolah why screw around with it? Truck axles are plentiful and cheap, and pre-'81 they were still available with the 4.5" (car) bolt pattern, though there are 5" pattern rears out there as well. The only difference between the truck axle and the C-car axle is that the trucks were oversprung (leaf sits atop the axle) and the C-barge axle is undersprung. If you gotta weld a new pair of perches anyhow, you might save big bucks looking under trucks. Oh, and if you do need new perches, get the Moroso units rather than the Mopar Performance ones. For some reason, the MP perches have an oversize center hole while the Moroso pair has the proper register for your leaf-springs' center bolts. :huh: Unless, of course, you have iso-clamps, which I don't think you do.

 

[project74]

Thanks Jass I had the guy do a whole bunch of measurements including measuring from the flange to the perch on both sides and everything seems to check out ok. I posted a couple of pics just because. Looks like it could be a good piece. It's located in Maryland which is about 8 hrs from me so the wife and I are gonna make a weekend road trip out of it. I sent him $25 to hold it for a couple weeks so no big dollars lost. Guy was really cool about holding it and we had a pretty good talk, seems like a decent, honest cat. I'll do the physical tests when I get there and if it turns out to be not as good as stated I'll either cut my offer or just consider it a nice weekend away from the kids.